Remove useless (and conflicting) constant

Author: lloeki

Matrixfile

@@ -2,7 +2,7 @@
 # frozen_string_literal: true
 
 # rubocop:disable Layout/HashAlignment
-TEST_METADATA = {
+{
   'main' => {
     ''         => '✅ 2.5 / ✅ 2.6 / ✅ 2.7 / ✅ 3.0 / ✅ 3.1 / ✅ 3.2 / ✅ 3.3 / ✅ 3.4 / ✅ jruby',
     'core-old' => '✅ 2.5 / ✅ 2.6 / ✅ 2.7 / ✅ 3.0 / ✅ 3.1 / ✅ 3.2 / ✅ 3.3 / ✅ 3.4 / ✅ jruby'